Studies Look at Off-Hours MI, Bad Air and ACS

Action Points

Showing up at the hospital with an acute MI at night or on a weekend was associated with a greater risk of dying, and long-term exposure to particulate air pollution appeared to increase the risk of acute coronary syndrome.

Although the relative increase was small, the authors calculated that one out of every 27 in-hospital deaths and one out of every 29 deaths within 30 days could be avoided if the issue with off-hours presentation could be resolved, assuming the relationship is causal.

Showing up at the hospital with an acute myocardial infarction (MI) at night or on the weekend was associated with a greater risk of dying, and long-term exposure to particulate air pollution appeared to increase the risk of acute coronary syndromes, two meta-analyses published in BMJ showed.

Worse Outcomes for Off-Hours MI

Some, but not all, previous studies -- including one conducted at a New Jersey hospital -- have suggested that patients with acute MI have poorer outcomes when they arrive at night or on the weekend, possibly related to delays in treatment or staffing issues.

Henry Ting, MD, of the Mayo Clinic in Rochester, Minn., and colleagues set out to get a better idea of the magnitude of the relationship by pooling data from 48 studies with a total of nearly 1.9 million patients.

Although the relative increase was small, the authors calculated that one out of every 27 in-hospital deaths and one out of every 29 deaths within 30 days could be avoided if the issue with off-hours presentation could be resolved, assuming the relationship is causal.

Part of the association could be related to treatment delay, as the likelihood of receiving percutaneous coronary intervention within the recommended 90 minutes was significantly lower at night and on the weekend (OR 0.40, 95% CI 0.35-0.45).

"Clinical performance measures may need to account for differences arising from time of presentation to a healthcare facility," Ting and colleagues wrote, noting that their study was limited by the potential for residual confounding, the high heterogeneity across included studies, and the possible overlap of patients in various cohorts.

In an accompanying editorial, Lauren Lapointe-Shaw, MD, and Chaim Bell, MD, PhD, of the University of Toronto, wrote, "To properly evaluate the quality of healthcare delivered at all times, we must refine our methods of risk adjustment to include time to presentation and severity of illness. Future studies should try to identify specific deficits in the care pathway during off-hours, allowing differences in outcomes to be linked to differences in processes."

Giulia Cesaroni, MSc, of the Lazio Regional Health Service in Rome, and colleagues turned to the ESCAPE project to examine whether long-term exposure to different types of air pollution is associated with greater risks of acute coronary syndromes.

They performed a meta-analysis of 11 European cohorts from five countries that included a total of 100,166 people who did not have a history of coronary disease at baseline. Through an average follow-up of 11.5 years, 5.1% had an acute MI or developed unstable angina.

In the fully adjusted model, only one type of air pollution -- particulate matter measuring less than 10 µm (PM10) -- was associated with a risk of events. For every 5 µg/m3 increase in the estimated annual exposure, there was a 12% greater risk of having an acute coronary syndrome (HR 1.12, 95% CI 1.01-1.25).

Particulate matter measuring less than 2.5 µm (PM2.5) and PM10 were both associated with greater risks of acute events in analyses limited to exposures below the annual European limits for the two pollutants of 25 and 40 µg/m3, respectively.

"The results of this study, together with other ESCAPE findings, support lowering of European limits for particulate air pollution to adequately protect public health," the authors wrote, while acknowledging that the analysis was limited by potential residual confounding, heterogeneity across study populations, and the use of administrative databases to gather most of the outcomes.

In an accompanying editorial, Michael Brauer, ScD, and G.B. John Mancini, MD, of the University of British Columbia in Vancouver, wrote, "The important impact of air pollution on cardiovascular disease ... supports efforts to meet existing and even more stringent air quality standards to minimize cardiovascular morbidity and mortality. A specific focus on the mitigation of other widely recognised risk factors for cardiac events in areas where poor air quality presents an additional risk might also be warranted."

The study on off-hour presentation was funded by the Mayo Clinic Division of Cardiovascular Diseases, Mayo Clinic Quality Academy, Mayo Clinic College of Medicine, and Mayo Clinic Center for Science of Healthcare Delivery.

Ting and colleagues reported that they had no conflicts of interest.

The study on air pollution has received funding from the European Community's Seventh Framework Program. For the Finnish part, additional funding came from the Academy of Finland. The four Swedish cohorts were partially funded by the Swedish Environmental Protection Agency, the Swedish Council for Working Life and Social Research, and the Swedish Heart-Lung Foundation. The SALT cohort was additionally supported by the NIH. The 60-year cohort was additionally funded by the Stockholm County Council and the Swedish Research Council. The SDPP cohort was additionally funded by the Stockholm County Council; the Swedish Research Council; the Swedish Diabetes Association; and the Novo Nordisk Scandinavia. The Heinz Nixdorf Foundation, the German Ministry of Education and Science (BMBF), the German Aerospace Center (Deutsches Zentrum für Luftund Raumfahrt (DLR)), and the German Research Foundation for their generous support of Heinz Nixdorf Recall study. The KORA research platform and the MONICA Augsburg studies were initiated and financed by the Helmholtz Zentrum München, German Research Center for Environmental Health, which is funded by the German Federal Ministry of Education and Research and by the State of Bavaria. The SIDRIA cohort study was partially funded by the Italian Ministry of Health.

Cesaroni and colleagues reported that they had no conflicts of interest.

Lapointe and Bell reported that they had no conflicts of interest.

Brauer reported that he has collaborated with some of the authors of the study on unrelated topics. Mancini did not report any conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner